You need to remove a few bricks higher than your opening and attach a steel Lentil about 1/2 brick past the opening on each side. They prevent future sagging.If the fellas who laid the brick used Tabs to support them every so often it should hold tight where you remove them. If its close to the roof line its not a lot of extra courses above if they do fall. Do not hammer or chisel them out. That makes cracks that spread like windshieldMark the 4 corners inside and hammerdrill pilots so you see them outside. Use a diamond blade saw for the cuts. This is assuming they used a heavy Portland mix for mortar like most verneers are. If the mortar is dusty its a different story, just rake some dust out untill 1 pries out and repeat.